Telephone repeater



B. C. GROH.

TELEPHONE REPEATER. APPLICATION EILED MAR. 13. 1916.

1,416,663. 7 Y Patented May16,1922.

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Patented May 16,1922.

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BERNARD C. GROH, OF ST. PAUL, MINNESOTA, ASSIGNOR TO AUTOMATIC ELEC'ITRIC COMPANY, OF CHICAGO, ILLINOZS, CORPORATEON 013' ILLINGIS.

TELEPHONE REPEATER.

' Application filed March 13, 1916;

citizen of the United States of America, and:

resident of St. Paul, Ramsey County, Minnesota, have invented a certain new and useful Improvement in Telephone Repeaters, of which the following is a specification;

pulse repeater for automatic or semiautomatic telephone systems, and it relates morespecifically to arepeater adapted ior use ina common battery telephone system in which the automatic switches are controlled over two sides of the line in series.

An object of? my invention is to provide a repeater in which positive and eiiicient transmission ot'. electrical impulses is secured and the talking circuit upon the response of the called substation;

A further object of my invention is the provision oil"; a repeater to operate on trunk lines where the length of the trunk line is such that it is not satisfactory to send the original impulses over the entire distance to control and operate automatic switches and in which the transmission of voice currents is greatly facilitated because of the removal of bridges from across the trunk line.

To the foregoing and other useful ends my invention consists of. matters hereinafter set forth and claimed.

In the accompanying drawings Fig. 1 represents ageneral layout oi the system, in which I have chosen to illustrate my invention. 'le'terring to Fig. 1 it is assumed that the automatic substation A, whose line terminates in the exchange X, desires connoction with the automatic substation A, whose line terminates in apparatus at exchange Z. It is further assumed that the exchanges X and Z are at such a distance apart that satisfactory operation, in setting up a connection, is not obtained. By the addition of my improved repeater, on the trunk line at exchange Y, which is between exchanges X and Z, highly efficient results are secured, both as regards the transmis sion of electrical impulses and of voice currents.

Figs. 2, 3 and 4: taken together represent a. complete cormection between a calling Specification of Letters Patent.

Patented litany 16, 1922.

Serial No. 83;838.

subs ation A and a called substation A embodying theprinciples of my invention.

Flgs. 5 and 6 illustrate the operating and talking circuits of the repeater R.

The system herein illustrated is of a well known type, known as a two-wire system,

i and is equipped with individual or line My invention relates to an nnproved 1m-- switches G divided into groups, each group controlled by a masterswitc-h I). There are alsoprovided the group selectors E and E, repeaters F and B- and connectors H. The current for operating and talking purposes being supplied by the batteries B, B, and The subscribers stationv A is connected. with the central ofiice through the line conductors 1' and 2, which terminate in a line switch C, said switch being one of a group in which all bridges are removed irom across of switches governed by the master switch I).

By means of the line switch (.l the line is extended to the selector E. The selector E selects the repeaters F and R which control the selector E at exchange Z. Selector E extends the connection to the connector H which completes the connection to called subs ,1ll6l".3 telephone A.

he telephone at the substation A is provided with a receiver transmitter i, ringer 5 and condenser 6. It is also provided with a suitable impulse-sending device similar to that shown: and described in United States Letters Patent to J. G. Blessing, No. 1,119,394, granted December 1, 1914, and comprises an impulse-wheel 7, springs 8 and a dial (not shown) which has holes around its periphery for convenience in rotating. The dial controls the impulse-wheel to open and: close the impulse springs 8 a number of times corresponding to the digits of the called number.

The line switch C and the master switch D are of the general type oi" line and master switches disclosed in British patent to B. W. James, No. 26,301 of 1906 and of the type shown in British patent to T. G. Martin, Flo. 14-19 0 51910, being however, more particularly ot' the form shown in United States Letters Patent to F. Newtorth, (J12, No. 13,901, reissued April 13, 1915. As herein represented. the line switch 0 comprises among other details, a. plunger (not shown) which is attached to the end of a plunger arm 9, that is controlled by the magnet 1U.

The magnet 10 comprises a pull-in winding 11 and a holding or cut-off Winding 12. The pull-m winding 11 is only strong enough to operate the cut-off armature 13 but is strong enough to hold the plunger arm 9 in its operated position after it has been operated by the pull-in winding. The line relay 1 1 controls the circuit of the pull-in winding 11. hen the plunger arm is attracted by the n'iagnet 10 the plunger is thrust into a group of bank springs 15, 16, 17, 18, 19, 20, 21, and 22, forcing them into contact in pairs. Although only one set of springs, 15 to 22. is shown, each switch is provided with a plurality of such sets, each set forming a terminal of a separate trunk line leading to a selector such as E. These sets of trunk line terminals are, of course, multipled to the corresponding sets in the banks of the other line switches in the same group. The plungers of all the line switches of the group which are controlled by the master switch D engage a plunger shaft, through the medium of which said master switch normally maintains the plungers opposite the: terminals of an idle trunk line.

The selector E is of the general type of selector switch disclosed in United States Letters Patent No. 815,321, granted to Keith, Erickson and Erickson, March 18, 1906, the side-switch being dispensed with and the circuits modified in order to adapt the switch for operation in a system in which the central oflice apparatus is controlled by impulses delivered over two sides of the line in series. Among other details the selector comprises the line relay 28, release relay 2 1, vertical magnet 25, rotary magnet 26 for moving the switch shaftto which is attached the wipers 27. 28 and 29. There is also provided the switching relay 30, controlling relays 31 and 32, and the release magnet 33. The springs 34 and 85 are closed when the switch sha l't moves one step from its lowest or normal position.

The repeater F comprises a line relay 36, slow relays 257 and 38, battery reversing relay 39, impedance coil 40 and condensers C and C The line relay 36 is bridged across the trunk line extending from the selector E to the repeater, and is arranged so that, when its armature operates in accordance with the impulses from the subseribers station A, it opens and closes the bridge across the trunk extending to the repeater R, a corresponding number of times. Among the functions of this repeater is to receive the electrical impulses from the subscribers impulse sender and repeat them to the repeater t which is further along the trunk. .Tiurthermore, it supplies battery current to the calling line for talking purposes and maintains a holding circuit for the switches C "and E.

The trunk line conductors 11 and 42 extend from the repeater F to the repeater R. The repeater R has a line relay 13, slow relays 4H and 4:5, slow-acting controlling relay &6, polarized relay 17 resistance coil 18 and condensers C and C The repeater R is connected to the selector E by means of the trunk line conductors 19 and 50. The selector E is similar to the selector E and comprises a line relay 51, release relay 52, vertical magnet 53, rotary magnet 54, switching relay 55, controlling relay 56, slow relay 57 and release magnet 58. The switch shalt (not shown) carrying the wipers 59, 60 and 61, has a vertical and rotary movement controlled by the magnets and 54. The switch shaft, when in its lowest position, separates the springs 62 and and 63 andv allows them to engage upon its first step. The selector extends the connection to the connector H which latter is of the type disclosed in United States Letters Patent No. 815,176 granted March 13, 1906 to Keith, Erickson & Ericksombut is moditied to adapt it for use in a. two wire system. Among other details the connector comprises a line relay 61, release relay 65, vertical magnet 66, rotary magnet 67, private magnet 68, back bridge relay 69, ringer relay 70, )rivate control relay 71, and ringer cut-off relay 72. This switch has the usual shaft, carrying the wipers 78, 74 and 75, having vertical and rotary movement controlled by the vertical and rotary magnets.

The line switch C and the substation A are the same as line switch and substation A.

Having given a general description of the apparatus involved in the system and as the line switch, selector, connector and repeater 1* herein shown, are well known to those versed in the art, their operation will be described in a more or less general manner. I will. now describe how a subscriber at substation A may obtain connection with a subscriber at substation A, the number of which we will assume to be 2220.

Upon the removal of the receiver 3 from the switch hook the line switch C is tripped in the well, known manner, so as to thrust its plunger into the terminal bank thereby forcing springs 15, 17 19 and 21 into contact with springs 16, 18, 20 and 22, respectively. The calling line is thus placed into connection with the selector switch E, energizing the line relay 23, which pulls up and closes a circuit to release relay 24. Release relay 2 1, upon energizing, supplies a holding ground G through springs 76, springs 18 and 17, thence over two paths, one leading through the hold-in winding 12 to the battery B, the other of which leads to the private normal conductor 7 7 to the private contacts of the connectors adapted to seize the line of substation A. Upon the operation oi the calling device for the first digit, the

Cir

circuit of the line relay 23 is momentarily opened twice at the impulse springs 8, therebydeenergizing said line relay a corresponding number of times to'cause the selector to he stepped up two steps, in the well-known manner, opposite the second row of contacts in which terminate the trunk lines Leading to the repeater F, whereupon the magnet 20 operates in the usual manner to rotate the shaft wipers onto an idle trunk line whereupon the switching relay 30 energizes to extend the line connection to the line relay 36 of repeater F.

The line relay 36, upon energizing, closes a circuit to the slow-acting relay 37 which extends from ground G through springs 78 and 79 and the relay 37 to the battery B. The relay 37, upon energizing, supplies a holding ground for the selector E and line switch C to relieve .the ground G which is removed when the switching relay 30 opens the circuit to relays 23 and 24; The holding ground is furnished over a circuit that extends from ground G through springs 80 to a point 81, wiper 28, to a point 82, thence over two paths, one of which extends through springs 83 and the switching relay 30 to battery, the other path extends from the point 82, springs 35 and 84, springs 18 and 17 and the holding winding 12 to battery B. Another circuit is closed at this time extending from ground G through springs 80, point 81, right-hand winding of relay 39 to the battery B; A further result of the energization of relay 37 is the closure of springs 85, thereby preparing a circuit for the slow relay 38. Another result of the energization of line relay 36 is the closure of springs 86- thereby closing a circuit for line relay 43 of repeater R which extends from ground G through lower winding of relay 43, springs 87 and 88, conductor 42, springs 86, impedance coil 40, left-hand winding of relay 39, return conductor 41, springs 89 and 90, upper winding of relay 43 to the battery B". Bot-h windings of relay 39 now carry current which is in the direction to oppose each other and the armature remains unoperated. The line relay 43 energizes over the above circuit and closes a circuit to slow acting relay 44 extending from ground Gr" through springs 91 and 92 and the said relay 44 to the battery B. Relay 44, upon energizing, prepares, at its springs 93, acircuit for slow relay 45. A further result of the energization of line relay 43 is closure of a circuit to the selector E extending from ground G through the lower winding of line relay 51, springs 94, conductor 50, springs 96, lower winding of relay 47, springs 97 and 98, upper winding of relay 47, springs 99 and 100 of relay 45, return conductor 49, springs 95 and the upper winding of line relay 51 to the battery B The relay 47 is a magneticallypo1arized relay, and attracts its armature in one direction when it receives current of one polarity and in the other di rection whenit receives current of opposite polarity. The s n'ings 101 of said relay 47 are normally separated and it receives current at this time to maintain them separated. The line relay 51 of selector E energizes over the above circuit and closes a circuit for the release relay 52.

The central oliice apparatus is now in condition to receive the second digit of the called number, whereupon the calling device is operated in the usual manner, opening the circuit of the line relay 36 of the repeater F, twice momentarily. The slow-acting relay 37 retains its armature in the operated position during the momentary interruptions of its circuit by relay 36 responding to the impulses. 'llheretore, the ground (i is held upon the release trunk, thus holding up the preceding switches. Each time that the line relay armature drops back, a cil'Cllit is completed from ground G through springs 78 and 102 springs and slow relay 38 to the battery B. The result is that the. first time the circuit is broken for the second digit, relay 33 closes a direct bridge across the trunk, and since said relay 33 is slow-acting this bridge is maintained closed at springs 103 and 104 during the subsequent impulses of the digit. Each time the armature of line relay 36 drops back in responding to the momentary interruptions of the calling device, it opens this bridge at springs 86 and thus repeats impulses to the repeater R. It is well to note that impedance coil 40 and left-hand winding of relay 39 are shortcircuited by springs 103 and 104 during the transmission of impulses. The right-hand winding of said relay continues to carry current but is of insuflicient strength. to pull up the armature.

The line relay 43 of repeater R responds to the momentary interruptions of its circuit. The slmv-acting relay 44 retains its armature in the operated position during the transmission of impulses. 'lhereiore the first time the armature of? line relay 43 drops back in responding to the impulses, a circuit is completed which extends from grouml G through springs 91 and 105, springs 93 and the relay 45 to battery B. The relay 45, upon energizing, closes a direct bridge across the trunk line. conductors 49 and 50 at springs 100 and 106 which includes springs 96 of the line relay Since said relay is slowacting, it maintains said bridge closed during the subsequent impulses. The line relay 43 in responding to the impulses transmitted from repeater F, opens the bridge at springs 96 to repeat impulses to the selector switch E. The selector line relay 51 thus operated to transmit impulses to the vertical magnet 53 to thereby step the shaft wipers to the second level of back contacts leading to connectors such as H. The selector stops upon the first idle contact, in the well known manner, whereupon the switching relay 55 operates to switch the line circuit through to the connector H, to energize the line relay 64'. The line relay 641-, upon energizing, closes a circuit for release relay 65, which, upon energizing, supplies a holding ground upon the release conductor to selector E which extends from ground U through springs 107, release conductor 108, wiper 60, springs 109 of relay56 and the relay 55 to the battery B The selector E is thus held in its operated position. Another result of the energization of relay is the opening of the circuit of the release magnet 110 by disengaging springs 111 and 112 and the preparation. of the vertical magnet circuit by the closing oi springs 111 and 113.

The calling device may now be operated for the third digit 2, deenergizing the line relay 36 of: repeater F, twice, which deeuergizes line relay 43 0t repeater R, twice, which in turn deenergizes the line relay 6'1 ot' the connector twice. The armature .01 said line relay 6% upon falling back transmits two impulses to the vertical magnet over a circuit which extends from ground G through springs 11% and 115, springs 111 and 113, relay 71, vertical magnet 66, side-switch wiper 116 to the battery B The vertical magnet receives two impulses over this circuit and operates to raise the switch shaft and wipers two steps to a position opposite the second level of bank contact in which are situated the terminals 01' the called subscribers line. The slow controlling relay 71 is energized by the first impulse and maintains its armature in its operated position during the subsequent impulses of the digit. In its energized position the relay 71. closes an energizing circuit for the private magnet 68. The pause, after the impulses have been delivered, permits the controlling relay to deenergize which allows the private magnet to fall. back and causes the side switch to pass to second position. The side switch wiper 116 upon passing to second position transfers the battery connection from the vertical magnet 66 to the rotary magnet 67. The subscriber now operates his calling device for the last digit 0, thus sending in ten impulses and thereby operating the line relay 64 of the connector in the same manner as previously described. The relay 64- operates a corresponding number of times to close a circuit through the rotary magnet 67, rotating the line and private wipers ten steps onto the contacts 01 the desired line. The relay 71 and private magnet 68 operate in the same manner as for the preceding digit. The private magnet upon deenergizing permits the side switch to pass from second to third position. When the side switch wiper 117 passes to third position an energizing circuit is established for the cut-off winding 118 of the called subscribers line switch which extends from ground G through side switch wiper 117 (in third position), private wiper 741 and the cut-off winding 118 to battery B The side switch wipers 119 and 120, upon passing to their third position contact points, complete the line circuit to the called line. Side switch wiper 116, upon engaging its third position contact, closes a circuit that extends from ground (1 through interrupter 121, ringing relay 70, springs 122 and side switch wiper 116 to the battery B The ringer relay 76 is energized intermittently over the above circuit and operates to separate the called line from the calling line and to bridge the ringing current gen erator R6: across the called line to signal. the called subscriber. Upon the subscriber at substation A removing his receiver to answer the call, and as soon thereafter as the ringing relay deenergizes if it happens to be energized at the time, a circuit to the back bridge relay 69 is closed at substation springs 123. Said circuit being traced from ground G through the left hand winding of relay 69, springs 123 of: private magnet 68, over heavy conductor through contact springs of ringing relay 70, wiper 75, to and through the called substation back over wiper 73, another pair of contact springs of ringing relay 70, springs 124 of private magnet 68 and the righthand winding of bark bridge relay 69 to the battery B Talking current is supplied over the above traced circuit to the called subscriber. Upon the energization of said back-bridge relay 69, a circuit is closed from ground G through side switch wiper 117, springs 125 and relay 72 to battery B Relay 72, upon energizing, open the circuit of ringing relay at springs 122, and at springs 126 closes a locking circuit for itself which extends from ground G through side switch wiper 117, springs 126 and the relay 72 to the battery B A. t'urther result of the en ergization of back bridge relay 69 is the reversal of the direction of current flow in the direction of the calling subscriber. This reversal of current, of course, flows through polarized relay 47 and is in the opposite direction to the previous current, thereby causing said. relay to pull over its armature in the direction to close the contacts at 101. A, circuitis then closed from ground at G? through contacts 101, relay 16 to the battery B. The relay' 16, upon energizing, places the line relay 48 in another or local circuit to maintain it energized. This circuit for relay 13 extends fromground G through springs 87 and 127, resistance 48, and the upper win-ding of relay 4:3 to the battery B, A further result of theenergization of relay 46 is the shifting of springs 89, 97 and 8'7 out of engagement with springs 90, 98 and 88 and into engagement with springs 128, 129 and 127, whereby the upper winding of relay 1'? is bridged across the con denser C and the lower winding is bridged lower winding of relay 47, springs 96 of relay Y the called party removes his receiver.

circuit illustrated in Fig. shows me condi- 43, return conductor 50, springs of relay '55, line wiper 61, springs 137 and 138 of relay 69 and the upper winding of line relay 64 to the battery B The circuit shown in Fig. 5 illustrates the condition of repeater R before The tion of repeater B after the called party answersi The relay 16 is preferably made slow-acting so that if thecalling subscriber operates the calling device after the called subscriber has answered, the relay as will not respond to the momentary interruptions of its circuit caused'by the operation of relay 17. It is thus seen that the repeater It is free of bridges after the called party answers. The reversedbattery as traced from the connector is supplied through the windings of relay 17 along the trunk conductors l1 and 4-2 through the left-hand winding of relay 39 in series with impedance coil 10. The two windings of relay 39 will now carry current in the same direction, whereby the armature of said relay is attracted, which reverses the direction of flow of battery current in the calling subscriber s line. The subscribers may now converse and after the conversation is finished the connection is released by the calling subscriber hanging up his receiver, thereby breaking the line circuit at springs 130, at substation A. The opening of the line circuit at substation A, opens the circuit of the line relay 36 of repeater F. llpon relay 36 deenergizing, the circuit of slow ac ing relay 3? is opened, thus removing the holding ground G from the switching relay of selector E as well as from the holding winding 12 of the line switch C. Upon switching relay 30 falling back a circuit is closed tothe release magnet 33 which extends from ground G through springs 131, springs 132, springs 133, springs 34 and the release magnet 33 to the battery 13. The release magnet 33,-upon energizing, restores the switch shaft and wipers to their normal position, and its own circuit is opened at springs switch,

34: when the shaft reaches its normal position. The holding winding 12 of the line upon deenergizing, permits the plunger-arm 9 to withdraw the plunger from the bank of contacts and also allows the cut-off arm 13 to be released to once more bridge the line relay ll across the line.

The deenergization of line relay 36 of repeater F, by the separation of springs 86 opens the circuit of line relay assuming the called subscriber restores his receiver. to its switchhook ahead of the calling subscriber. Relay 13, upon decnergizing, opens the circuit of relay 4% and at springs 96 opens the energizing circuit of line relay 64: of connector H. Relay 6-1, upon decnergizing breaks the circuit of release relay 65 which removes the holding ground G from the switching relay of selector The se lector E releasing in the same manner as was described in connection with selector ls). A further result of the deenergization of relay 65 is the closureof a circuit extending from ground G through springs ill-Ll and 115, springs 111 and 112, springs 134- and the release magnet 110 to the battery B The release magnet, upon eiiergizing, restores the shaft and side-switchwipers to their normal position and its own circuit is opened at springs 134: when the shaft reaches its lowest or normal position. The circuit of cut-off winding 118 of switch C is broken when the connector releases thereby placing the line relay of the line switch across the line. If, however, the calling subscriber places his receiver upon the switchhooh ahead of the called subscriber, then the release of the connector is controlled direct from the repeater 1 instead of by the repeater It. In that event when the line relay 36 of repeater F separates springs 66. the energizing circuit including relay 1-1 of repeater R and line relay 6% of the connector 1S broken.

The relay lflupon deenergizing, opens the contact of springs 101, thereby deenergizing relay 16. Relay -16, upon decnergizing, places the line relay again across the trunk, the circuit of which is now broken, which causes said relay 4-3 to decnergizo. Upon the relay 1-3 deenergizing, the circuit for relay 4: 1 is opened and the repeater relays are placed in their normal rendition. The connector ll controls the release of the selector E and releases itself in the same manner as hereinbefore described.

Assuming that the called line busy there will then be a guarding ground potential upon the connector private bani; contact. The connector I l upon attempting to coin plete a connection witl'i the busy line. will maintain its side switch wipers in the second position thus preventing completion of the connection. As soon as the relay 71 (teenergizes after the last digit of impulses hare been delivered and while side sw tch i n second position a circuit is closed from ground upon the connector private bank contact, through private iper "Tl, side switch wiper 117 (in second position), springs 139 and 1&0, busy relay 1 11, springs 142, private magnet 68 to the battery B The busy relay 1%], upon energizing, terms a locking circuit for itself extending from ground G through springs 1 1-3, springs 14 1 and MO of relay 141, the said relay 1&1, springs 142 and the private magnet 68 to the battery B A further result oi the energization of the busy relay is the opening of the rotary magnet circuit at springs 1 16 and the closing of springs 145, whereby a busy tone from the busy machine Q is furnished to the calling subscriber by way it side switch wiper 120, conductor 50, conductor 42, line conductor 1, to and through the subscribers substation, return conductor 2 to the negative pole of battery, whereupon the receiver is replaced on the switch hook and the connection is released in practically the same manner as previously described.

In connection with the repeater B it is seen that as soon as the called subscriber removes his receiver from its switehhook in answering the call, the relation of windings of relay 1'? with respect to the trunk is altered. Before the called party answers the relay 4? is bridged across the called side of the repeater as shown in Fig. After the called party answers the front bridge relay 43 is removed from the trunk and placed in a local circuit, while the windings of relay 4? are placed in multiple with the condensers U and C as shown in Fig. 6. It is thus seen that all bridges are eliminated from the repeater R during talking and the transmission of voice-currents is greatly facilitated.

It is thus evident that I have devised a very eflicient form of repeater t'or transmitting electrical impulses during the setting up of the connection and one in which all bridges or bypaths for voice currents are removed during the talking stage of the operations.

lVhile I have illustrated my invention in connection with a full automatic telephone system of a particular type, it will be readily apparent that my repeater is equally as well adapted for use in other types 01 automatic systems, or with semiautonnitic telephone systems. Various modifications and changes in the repeater itself will likewise be suggest ed to those skilled in the art and come within the broader aspects of my invention.

What I claim as my invention is:

1. In a telephone system, a calling and a called line, means including a plurality of automatic switching mechanisms for connecting said lines, a relay for controlling the progressive motion of one of said mechanisms to extend a connection to another one of said mechanisms and for then controlling said other mechanism over said extension, said relay normally connected in bridgeo'f the line conductors at one of said mechanisms, said bridge including a battery and said relay in series, and a relay actuatedv upon theclosure of the called line circuit for causing the disconnection of said controlling relay from in bridge of the line, said bridge so connected normally that there is no flow of current through any :part thereof. Y

2. In a telephone system, a calling and a called line, means including a repeater and automatic progressively movable switches controlled thereby for connecting said lines in a metallic talking circuit, a line relay for controlling the progressive motion of one of said switches to extend a connection to another one of said switches and for then controlling said other switch over said extension, said relay normally in bridge of the line conductors at said repeater, said bridge including a battery and said relay in series, and means for automatically opening said bridge during conversation, said bridge so connected normally that there is no flow of current throu h an art thereof.

3. In a telephone system, a calling and :1 called line, means including a repeater and automatic progressively movable switches controlled thereby for connecting said lines in a metallic talking circuit, a line relay for controlling the progressive motion of one of said switches to extend a connection to another one of said switches and for then controlling said other-switchoversaid extension,said relay normally in bridge of the line conductors at said repeater, said bridge including a battery and said relay in series, and means controlled by the response of the called subscriber for disconnecting said relay from in bridge of the line, said bridge so connected normally that there is no flow of current through any part thereof.

4. In a telephone system, a calling and a called line, means including a repeater and automatic qn'ogressively movable switches controlled thereby tor connecting said. lines in a metallic talking circuit, a line relay for controlling the progressive motion of one of said switches to extend a connection to another one oil. said switches and for then controlling said other switch over said extension, said relay normally in bridge of the line conductors at said repeater, said bridge including a battery and said relay in series, a second relay in said repeater for opening said bridge during conversation, and means for controlling said second relay from said switch over the line conductors extending between the said switch and repeater, said bridge so connected normally that-there is no flow of current through any part thereof.

5. In a telephone system, a temporarily s ahished c nnection between-a callin and a called line including arepeater, a line relay in said repeater controlling the maintenance of the connection, said line relay being normally included in a bridge of the line conductors at said repeater but temporarily disconnected therefrom, and local circuit for maintaining said line relay energized during conversation.

6. In atelephone system, means for connecting a calling and a called line including a repeater am; an automatic switch, means for closing a bridge across the line conductors at said repeater to prevent the release of said switch after the same has been operated, and means for opening said bridge during conversation and for closing the same over a different path.

7. In a telephone system. means for connecting a calling and a called line including a repeater and an automatic switch, means for closing a bridge across the line conductors at said repeater to prevent the release of said switch after the same has been operated, inductive windings in said bridge, means for opening said bridge and for con necting said windings serially in the line circuit, and second bridge across the line another point for preventing the release of said switch during conversation.

S. In a telephone system, means for connecting a calling and a called line including a repeater and an automatic switch, means for closing a bridge across the line conductors at said repeater to prevent the release of said switch after the same has been operated, means for automatically opening said bridge when the called subscriber answers, and additional means for preventing the release of said switch during conversation.

9. In a telephone system, means for connecting a calling and a called line including a trunk line comprising two inductively connected sections, a. repeater at the junction of said sections, a double wound controllin relay connected in a bridge of one section of the trunk line, and means for conductivcly uniting the conductors of said sections by way of the windings of said relay.

10. In a telephone system, means for connecting a calling and a called line including a trunk line comprising two inductively connccted sections, a repeater at the junction of said sections, a double wound controlling relay connected in a bridge of one section of the trunk line, and means controlled by the subscriber on the called line for conductively uniting the conductors of said sec tions by way of the windings of said relay during conversation.

11. In a telephone system, means for connecting a calling and a called line including a trunk line comprising two inductively connected sections, a repeater at the junction oi said sections, a double wound controlling relay connected in a bridge of one section of the trunk line, and circuit controlling mechanism for changing said relay in relation to said trunk line from bridged to series conncction.

12. In a telephone system, a trunk line comprising two inductively connected sections, the second section terminating in an automatic progressively movable switch, a relay in bridge of the first section and energized over the conductors thereof to close a control circuit over said second section for causing the progressive motion of said switch, means for operating said switch through the medium of said relay and control circuit to establish a talking circuit between a calling and called line, and means for automatically disconnecting said relay from in bridge of said trunk line during conversation, said bridge so connected normally that there is no flow of current through any part thereof until the conductors 01 said first section are connected together.

13. In a telephone system, a trunk line comprising two inductively connected sections, the second section terminating in an automatic progressively movable switch, a relay in bridge of the first section and cncr gized over the conductors thereof to close a control circuit over said second section for causing the progressive motion oi said switch, means for operating said switch through the medium of said relay and control circuit to establish a talking circuit between a calling and called line, means tor automatically disconnecting said relay from in bridge of said trunk line during conversation. and tor maintaining the same energized over a local circuit to prevent the release of the connection, said bridge so connected nor mally that there is no flow oi current through. any pa rt thereot until the conductors of said first section are connected together.

1-1. In a telephone system, a trunk line comprising two inductively connected sections, the second section terminating in an automatic switch, a relay in bridge oi the first section and energized over he conductors thereot to close a control circuit for said switch, means for operating said switch through the medium of said relay and con trol circuit to establish a talking circuit hetwecn a calling and called line, an inductive winding in said control circuit constituting a bridge of said second section, and automatic means for holding said second bridge open during conversation.

15. In. a telephone system, a trunk line comprising two inductively connected sections, the second section terminating in an automatic switch, a relay in bridge of the first section and energized over the conductors thereof to close a control circuit for said switch, means for operating said switch through the medium o1 sa d relay and coir trol circuit to establish a talking circuit between a calling and called line, an inductive winding in said control circuit constituting a bridge of s l second section, and automatic means ior holding both bridges open during conversation.

16. In a telephone system, a trunk line comprising two inductiyely connected sections the second of which terminates in an autonia'ic switch, a repeater at the junction of said sections, a line relay in bridge of the first section at sa d repeater, means For completing a second bridge across said first section at the far end thereof to energize said relay, :1 control circuit for said switch closed by said relay, an inductive winding in said control. circuit constituting a bridge of said second. section, means for interrupting said second bridge to operate said switch through the medium of said line relay and control circuit to establish a talking connection between a calling and a called line, and means for opening the bridge across the second section and for conductively connecting the conductors ot the two sections whereby said control circuit is maintained closed by way of said second bridge. 7

17. In a telephone system, a trunk line comprising two inductively connected sections the second of which terminates in an automatic switch, a repeater at the junction of said sections, a line relay in bridge of the first section at said repeater, means for completing a second bridge across said first section at the far end thereof to energize said relay, a control circuit for said switch closed by said relay, an inductive winding in said control circuit constituting a bridge of said second section, means for interrupting said. second bridge to operate said switch through the medium of said line relay and control circuit to establish a talking connection between a calling and called line, means for automatically opening both the line relay bridge and the bridge across the second section, and means for conductively uniting the conductors of the two sections whereby said control circuit'is maintained closed by way or? said second bridge.

18. In a telephone system, a trunk line comprising two inductively connected sections, the second section terminating in an automatic switch, a relay in bridge of the first section and energized over the conductors the-reel. to close a control. circuit for said switch, means for operating said switch through the medium of said relay and control circuit to establish a talking circuit between a calling and called line, an inductive winding in said control circuit constituting a bridge oi said second section, and automatic means operated over said control circuit for holding said second bridge open during conversation, a section of said control circuit extending over a part 01" said second section.

, it). In a telephone system, a trunk line comprising two inductively connected sections, the second section terminating in an automatic switch, a relay in bridge of the first section and energized over the conductors thereof to close a control circuit for said switch, means for operating said switch through the medium of said relay and control circuit to establish a talking circuit between a calling and called line, an inductive winding in said control circuit constituting a bridge of said second section, and automatic-means operated over said control circuit for holding both bridges open during conversation, a section of said control circuit extending over a part of said second section,

20. In a telephone system, means for connecting a calling and a called line including a trunk line comprising two inductively connected sections, a repeater at the junction of said s ctions, a controlling relay connected in a bridge of one section of the trunk line, and means for conductiyely uniting the conductors of said sections by way of the windings of said relay.

21. In a telephone system, means for connecting a calling and :1 called line including a trunl: line comprising two inductively connected sections, a repeater at the junction of said sections, a controlling relay connected in a bridge of one section of the trunk line, and means controlled by the subscriber on the called line for conductively uniting the conductors of said sections by way of the windings of said relay during conversation.

In a telephone system, means for con uecting a (f llll11g and a called line including a trunk line comprising two sections, a repcater at the junction of said sections, condensers inductively connecting said sections, a double wound controlling relay connected in a bridge oi? one section of the trunk line, and means controlled by the subscriber on the called line for conductively uniting the comluctors oi said sections during conversation by connecting the two windings of said relay in shunt of the said two condensers, respectively.

In a telephone system, means for connecting a calling and called. line including a trunk line comprising two inductively connected sections, a repeater at the junction of said sections, a controlling relay in said repeater in bridge of the first section. a second relay in said repeater in bridge of the second section, and circuit controlling mechanism for disconnecting one of said relays from the trunk line and for changing the other relay in relation to the said trunk line from bridged to series connection.

Signed by me at Paul, Ramsey County, Minnesota, this 7th day of March, 1916.

' BERNARD C. GROH. 

